relaxed_permissions not working on Ubuntu 22.04

[majorandras74]

Hello!

I use the Unionfs-fuse solution to separate static data from data generated during the game (save, score, setting, etc.) for games running over an emulator. In the past, there was a problem that caused the file created when writing to union to get stuck in the permission check (it was virtually 0 bytes in size and no permission bits were set to it (000)). This is solved by the "relaxed_permissions" option. Unfortunately, the problem came back when I switched to the latest Ubuntu release, 22.04. It's like the "relaxed_permissions" option doesn't work for some reason. Can you see what the problem might be? If you write what data you need I will try to provide it. Until then:

unionfs-fuse version: 2.3
(compiled with xattr support)
FUSE library version 3.10.5
using FUSE kernel interface version 7.31
fusermount3 version: 3.10.5

Thanks

[bsbernd]

I just updated one of my systems yesterday night, will test it in the evening today.

[rpodgorny]

please try again with the current (3.1 as of now) version, thanks!

[majorandras74]

Hello!

Tried with the latest version, but unfortunately the situation is unchanged.

unionfs-fuse version: 3.2
(compiled with xattr support)
FUSE library version 3.10.5
using FUSE kernel interface version 7.31
fusermount3 version: 3.10.5

Bye

[bsbernd]

It actually works as expected and would be unsual if not - this is a kernel fuse feature - by default we add in "default_permissions", which makes the kernel to verify if you are allowed to access a file. "relaxed_permissions" removes "default_permissions", unless started as root, this option is then ignored for security reasons.

Example

total 12K
drwxr-xr-x 2 bernd bernd 4.0K Aug 12 20:04 over
drwxr-xr-x 2 bernd bernd 4.0K Aug 12 20:02 root
drwxr-xr-x 2 bernd bernd 4.0K Aug 12 20:00 union

bernd@t420-work-1 unionfs>ll root/
total 4.0K
-rw-r--r-- 1 root root 5 Aug 12 20:02 file

bernd@t420-work-1 unionfs>ll over/
total 0

1. Without relaxed permission

unionfs -d -o allow_other,use_ino,nonempty,cow over=RW:root=ro union/
(-d for debug output and runs in foreground)

Other shell:

bernd@t420-work-1 unionfs>echo 1234 >union/file
bash: union/file: Permission denied

2. With relaxec permission

bernd@t420-work-1 unionfs>unionfs -d -o allow_other,use_ino,nonempty,cow,relaxed_permissions over=RW:root=ro union/

Other shell:

bernd@t420-work-1 unionfs>echo 1234 >union/file
bernd@t420-work-1 unionfs>

and this creates

bernd@t420-work-1 unionfs>ll over/
total 4.0K
-rw-r--r-- 1 bernd bernd 5 Aug 12 20:12 file

Hence, the feature works as expected.